<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<style>
    .bar {
        width: 20px;
        height: 20px;
        background-color: red;
        border-radius: 50%;
        animation: move 3s linear infinite alternate;
        position: absolute;
    }

    @keyframes move {
        0% {
           left: 0;
        }

        100% {
          left: 300px;
        }
    }
</style>

<body>
    <div class="bar"></div>
    <input id="file" type="file">
</body>

</html>